Rules to Better Microservices - 4 Rules

There are two common types of application architecture:

• Monoliths (aka N-Tier applications)
• Microservices

Monoliths have their place. They are easy to get going and often make a lot of sense when you are starting out. However, sometimes your app may grow in size and become difficult to maintain. Then you might want to consider Microservices...

Microservices let you break down your app into little pieces to make them more manageable, replaceable and maintainable. You can also scale out different parts of your app at a granular level.

.NET 6 and Azure have heaps of great tools for developing simple APIs and worker services in a Microservices pattern.

Watch the below video from 35:40 - 46:50

The tools of the trade

• .NET Worker Services make it easier to implement dependency injection, configuration and other syntactic sugar using the same patterns you are familiar with in other types of .NET applications
• Azure Container Apps give you a way to host different little subsections of the application
• Azure Functions gives you a great way to build applications in small, modular, scalable and easy to manage chunks. It provides triggers other than http to handle other common microservice patterns
• Minimal APIs give you a way to write APIs in just a few short lines of code

What's the point?

• Cost - Provides separation of scalability, keep the hot parts of your app hot and the cold parts of your app cold to achieve maximum pricing efficiency
• Maintainability - Keep code more manageable by making it bite sized chunks
• Simplify code - Write minimal APIs
• Deployment - Standardize deployment with containers
• Testing - Easier to find problems since they are isolated to a specific part of the app
• Cognitive Complexity - Devs can focus on one aspect of the app at a time
• Data - You can use the best way of storing data for each service
• Language - You can use the best language for each service

What's the downside?

• Upfront Cost - More upfront work is required
• Cognitive Complexity - While individual apps are simpler, the architecture of the app can become more complex
• Health Check - It's harder to know if all parts are alive
• Domain boundaries - You need to define the separation of concerns between different services. Avoid adding dependencies between services because you can create a domino of failures...a house of cards.
• Performance normally suffers as calls are made between services
• Without adequate testing it's harder to maintain
• Using multiple languages and datastores can be both more expensive to host and require more developers

What new techniques are required

• Contract Testing - To mitigate the risk of changes in one service breaking another, comprehensive tests that check the behaviour of services is required

Microservice architectures consist of a number of components

These often include:

• An API Gateway (think APIM, Ocelot, YARP, Azure Front Door)
• Support different types of frontends: Web, Desktop, Mobile
• Flexible deployment model in subsequent microservices
• Each microservice is in charge of its own data store
• Event driven
• VNet integration
• Messaging system (used to decouple services, think Azure SendGrid or ServiceBus)

When building distributed applications messaging is a common pattern to use. Often we might take a hard dependency on a specific messaging technology, such as Azure Service Bus or RabbitMQ. This can make it difficult to change messaging technologies in the future. Good architecture is about making decisions that make things easy to change in future. This is where MassTransit comes in.

MassTransit is a popular open-source .NET library that makes it easy to build distributed applications using messaging without tying you to one specific messaging technology.

.NET Messaging Libraries

There are several .NET messaging libraries that all abstract the underlying transport. These include:

• MassTransit (recommended)
• NServiceBus
• Rebus

There are also the service bus specific libraries:

• Azure Service Bus(not recommended)
• Amazon SQS(not recommended)
• RabbitMQ(not recommended)
• (and more)

Advantages of using MassTransit

✅ Open-source and free to use

✅ Enables swapping of messaging transports by providing a common abstraction layer

✅ Supports multiple messaging concepts:

• Point-to-Point
• Publish/Subscribe
• Request/Response

✅ Supports multiple messaging transports:

• In-Memory
• RabbitMQ
• Azure Service Bus
• Amazon SQS
• ActiveMQ
• Kafka
• gRPC
• SQL/DB

✅ Supports complex messaging patterns such as Sagas

Scenarios

Scenario 1 - Modular Monolith

A Modular Monolith architecture requires all modules to be running in a single process. MassTransit can be used to facilitate in-memory communication between modules in the same process.

This allows us to send events between modules and also request data from other modules.

Scenario 2 - Azure Hosted Microservices

When building microservices in Azure, it's common to use Azure Service Bus as the messaging transport. With minimal changes, MassTransit can be used to send messages to and from Azure Service Bus instead of using the In-Memory transport.

Scenario 3 - Locally Developing Microservices

When developing microservices locally, it's common to use containers for each service. However, some of the cloud based messaging services (e.g. Azure Service Bus) are not able to be run in a container locally. In this scenario, we can easily switch from using the Azure Service Bus transport to Containerized RabbitMQ transport

Demo Code

If you're interested in seeing MassTransit in action, check out github.com/danielmackay/dotnet-mass-transit

Choosing the right software architecture for your system is crucial for its success and maintainability. Making the wrong choice can lead to increased complexity, difficulty in scaling, and higher costs.

Popular Architectures

Here are some of the popular architectures and factors to consider when deciding the best fit for your project:

Clean Architecture

Clean Architecture emphasizes separation of concerns, making your system easier to maintain and scale. This architecture is designed to keep the business logic independent of the frameworks and tools, which helps in achieving a decoupled and testable codebase.

See more on Rules to Better Clean Architecture.

You can find our CA template on GitHub

Vertical Slice Architecture

Vertical Slice Architecture structures your system around features rather than technical layers. Each feature is implemented end-to-end, including UI/API, business logic, and data access. This approach improves maintainability and reduces the risk of breaking changes.

This modular approach to software development can introduce inexperienced teams to the idea of shipping features as functional units with no shared knowledge of the domain entities, infrastructure layer, or application layer within another subsystem, further preparing them for future develeopment environments that may use Modular Monolith or Microservices Architecture.

You can find our VSA template on GitHub

Modular Monolith

A Modular Monolith organizes the system into modules that encapsulate specific functionalities. While it runs as a single application, it retains some benefits of microservices, such as independent module development and testing. It’s a good middle-ground between a monolith and microservices.

See more on Rules to Better Modular Monoliths.

Microservices

Microservices architecture involves splitting the application into small, independently deployable services. Each service focuses on a specific business capability and can be developed, deployed, and scaled independently. This approach is beneficial for complex and large-scale applications with multiple teams working on different parts.

See more on Rules to Better Microservices.

Architecture Decision Tree

It's important to keep in mind that these architectures are not mutually exclusive.

Within a Modular Monolith Architecture, each module could be implemented using Clean Architecture or Vertical Slice Architecture. Similarly, a Microservices Architecture could use Clean Architecture or Vertical Slice Architecture within each service.

Also, from a pragmatic point of view a combination of Modular Monolith and Microservices might provide the best of both worlds. The majority of the system could be implemented as a Modular Monolith, with a few key services implemented as Microservices to provide scalability and flexibility where needed.

Factors to Consider

• Are your requirements certain?
  If requirements are likely to change, Clean Architecture or Vertical Slice Architecture can offer more flexibility.
• Do you have multiple domains?
  For applications with multiple domains, Modular Monoliths or Microservices can provide better separation and modularity.
• Do you have many teams? If you have many teams, Microservices or Modular Monolith can help in reducing inter-team dependencies and allow parallel development.
• Do you need independent deployments? If independent deployments are necessary, Microservices is the best choice due to its isolated nature.
• Do you need independent scalability? Microservices allow each service to be scaled independently based on its specific needs, which can be more efficient and cost-effective.
• Do you have DevOps maturity? Microservices require a mature DevOps culture to manage deployments, monitoring, and scaling effectively. Without this, the overhead can be overwhelming.
• Is the team experienced? The complexity of Microservices can be challenging for less experienced teams. Vertical Slice Architecture although simple, has fewer guardrails when compared to Clean Architecture and can lead to a mess if not managed correctly. This leads to recommending Clean Architecture for less experienced teams that need more structure.

Examples

Here are some practical scenarios to illustrate the decision-making process:

Scenario 1: Startup with uncertain requirements

Scenario 2: Medium-sized business with limited DevOps maturity

Scenario 3: Large enterprise with multiple domains and teams

By carefully considering these factors and understanding the strengths and limitations of each architectural style, you can choose the best architecture for your system, ensuring a balance between flexibility, scalability, and maintainability.